Rubber compound for golf ball and golf ball

ABSTRACT

A golf ball is provided that includes a molded resilient inner core made of a rubber compound and a polymeric cover surrounding the inner core. The rubber compound is a halo-butyl rubber polymer and a carbon black filler in an amount of 80% to 100% by weight of the total rubber component.

This invention relates to a rubber formulation and a rubber compoundwhich is suitable for use in making golf balls. This invention alsoextends to a golf ball having an inner core made of the rubber compound.

This invention relates particularly but not exclusively to a golf ballfor use in playing a compact indoor golf game and it will be convenientto describe it with reference to this example application. However it isto be clearly understood that the invention is not limited to its use inan indoor golf game and in fact the rubber compound and the ball couldbe used in a myriad of other applications including being used inoutdoor golf.

The game of golf is a very popular game and its popularity is constantlyincreasing. This has meant a strong demand for facilities to play thegame of golf. However the area of land occupied by standard golf coursesis considerable and thus in many environments and locations it may bedifficult to construct a full length 18 hole golf course. Further ifgolf courses are constructed outside of cities and in the country, itmay be difficult and time consuming for prospective golf players to getto the course for a game. Further the weather conditions in manycountries of the world prevent golf being played on normal outdoorcourses for many months of the year.

Accordingly there is potentially a huge demand for an indoor game ofgolf which can be located in densely populated areas with little spacefor sports facilities. There may also be a demand for a compact game ofgolf played on an outdoor course of reduced scale.

The applicant has already developed a compact golf game which isdisclosed in its international patent application no. PCT/AU90100398.The entire contents of this specification are explicitly incorporatedinto this document by cross reference. The game involves hitting a ballfrom a tee area against a rebound wall from where it rebounds to a greenarea positioned intermediate the tee and the rebound wall. The rebounddistance of the ball is a function of the impact characteristics of theball on the wall, eg velocity and trajectory of the golf ball. The wallis rigid and it is the ball which is specially designed to lose kineticenergy when it strikes the wall. This has the effect that the ball doesnot rebound as far as a standard golf ball and makes the game suitablefor playing indoors.

For the game to have lasting appeal and to reproduce the challenge ofthe great game of golf, it is obviously very important that the resultof any golf shot reflects the skill of a player and the quality of anygolf shot. It is also desirable that the ball have the look and feel ofa standard golf ball and create the same feel as a standard golf ballwhen struck by a golf club.

Previously the applicant used a ball having a resilient hollow innerball, eg like a squash ball, surrounded by a hard coating which is hardlike a standard golf ball but which is still capable of considerabledeformation.

However this ball tends to get too hot, especially in warm conditions,and when this happens the ball bounces too much off the walls. This hasthe potential to turn an indifferent golf shot into a good result andtherefore detracts from the quality of the game. Further the crisp feelof golf ball on club which occurs with a normal golf ball, diminishesover time with the applicant's ball.

Accordingly it would be advantageous if a ball could be found which didnot suffer from the shortcomings of the existing ball. The applicantsearched extensively for a ball which would meet its requirements butwas unsuccessful. Further applicant approached golf ball manufacturerswith a view to having a golf ball manufactured but was unsuccessful.Thus it had to take the initiative of guiding and procuring thedevelopment of a new ball.

According to an aspect of this invention there is provided a rubbercompound including a rubber component comprising essentially halo-butylrubber polymer; and carbon black in an amount of between 80% and 100% byweight of the rubber component.

A halo-butyl rubber polymer has been found to be suitable because it hasa low rebound co-efficient or resilience, particularly at temperatures5° C. to 40° C. This is a necessary property of golf balls produced forthe applicant's game because the game is played in a compact space andthe rebound distance has to be significantly lower than with a standardgolf ball. That is, significant energy must be absorbed from the golfball during impact.

Preferably the halo-butyl rubber polymer is chloro-butyl or bromo-butylpolymer.

Preferably the filler is N220 carbon black or N339 carbon black.

Carbon black is a reinforcing filler and in addition has the effect ofmodifying the hardness, resilience, and other physical properties of therubber compound.

Preferably the carbon black comprises 83 to 87% by weight of the totalrubber component, or preferably 85 to 95% by,weight, most preferably 88to 92% by weight, e.g. about 90% by weight.

The rubber compound may include at least one further filler, eg barytesand/or kaolin.

According to another aspect of this invention there is provided a rubberformulation for forming a resilient rubber compound, the formulationincluding:

a rubber component comprising essentially halo-butyl rubber polymer;

carbon black in an amount of between 80% and 100% by weight of therubber component; and homogenisation means for distributing the carbonblack homogeneously within the rubber component.

The halo-butyl rubber polymer may include any one of more of thepreferred features described above with reference to the first aspect ofthe invention. Similarly the carbon black may have any one or more ofthe preferred features described above with reference to the firstaspect of the invention.

For example the halo-butyl rubber polymer may be a chloro-butyl orbromo-butyl polymer and the filler may be carbon black, eg. N220 orN339.

Typically the formulation further includes vulcanising agents forvulcanising the rubber formulation during the processing thereof to formrubber. These vulcanising agents may include zinc oxide and/or a sulphurcompound such as disulphide, eg accelerants such astetramethylthiuramdisulphide and 2,2 dithiobisbenzothiazole.

The vulcanising agents facilitate crosslinking of the polymer chains, egby sulphur bridges.

The homogenising means may also include STRUTKOL 40 MS which facilitatesmixing of all components into the polymer.

The formulation may also include means for facilitating mixing andmoulding of the formulation, eg a blend of fatty acids and stearic acid.Yet further the mixing and moulding means may include a paraffinic ornaphthenic oil, eg PROPAR. The oils assist in mixing the formulation.

The formulation may also include micro-crystalline wax which assists inmixing.

According to yet another aspect of this invention there is provided amoulded resilient inner core for a golf ball, the core including arubber compound including a rubber component comprising essentiallyhalo-butyl rubber polymer, and a filler which is carbon black.

The carbon black may be present in an amount of between 80% and 100% byweight of the rubber component.

The halo-butyl polymer and the filler may include any one or more of thepreferred features as described above with respect to the first aspectof the invention.

According to yet another aspect of this invention there is provided agolf ball which includes:

a moulded resilient inner core- made of a rubber compound including a

halo-butyl rubber polymer and a filler which is carbon black, and apolymeric cover

surrounding the inner core.

The polymer and the filler of the inner core may include any one or moreof the preferred features as described above with reference to the firstaspect of the invention.

The cover is typically dimpled and has thickness and other propertiescomparable to the cover of a conventional golf ball. The golf ball hassimilar dimensions to a conventional golf ball and has an externalappearance which resembles that of a conventional golf ball.

In a preferred form the polymer of the core is chloro-butyl orbromo-butyl polymer and the filler is carbon black, eg N220 or N339.

Preferably the cover is an ionomeric polymer compound, eg. SURYLYN.

According to yet another aspect of this invention there is provided aprocess for making a golf ball, the process including:

providing a rubber formulation including a butyl polymer and at leastone

filler for modifying the resilience of the polymer;

mixing the formulation to distribute the filler homogeneously throughthe polymer;

passing the formulation through an open mill mixer to form sheeting; and

extruding the rubber through an extrusion die to form an extrudedarticle.

Typically the components in the formulation are solid or powdery andflowable.

Typically the method includes adding homogenising means to theformulation in the mixing step so as to disperse the carbon fillerhomogenously amongst the butyl polymer.

Typically the mixing step includes blending the formulation, eg in aninternal mixer, and then dumping it in an open mill mixer and sheetingit off to form a master batch.

Typically the mixing step further includes returning the masterbatch tothe open mill mixer, mixing it thoroughly, and then sheeting off a finalmix which is then used in the extrusion step.

Typically the accelerants are added when the masterbatch is returned tothe open mill mixer.

Typically the masterbatch is cooled, eg in a cooling tunnel and/or dipsolution, before being returned to the open mill.

Advantageously the method also includes the step of cutting a blank forforming an inner core of a golf ball from the extruded article after theextrusion step, and the further step of placing the blank in a mould andheating it to a temperature greater than 140° C. to mould the core.Preferably the inner core is moulded at a temperature of greater than155° C., eg about 160° C.

Preferably the method yet further includes moulding a cover of ionomericpolymer onto the inner core to form the cover of the golf ball, eg byinjection moulding.

A rubber compound and golf ball in accordance with this invention maymanifest itself in a variety of forms. It will be convenient tohereinafter describe in detail two examples of the invention. It is tobe clearly understood however that the specific nature of thisdescription does not supersede the generality of the precedingdescription.

Several formulations in accordance with the invention were mixed andcured to produce rubber compounds in accordance with the invention. Someexample formulations which were moulded into inner cores are describedbelow.

EXAMPLE 1

The composition of the formulation used in Example 1 is shown in thetable below.

PHR INGREDIENT (parts per hundred of the polymer) CHLOROBUTYL 1066100.00 (butyl polymer) STEARIC ACID 1.000 MICROWAX (micro-crystallinewax) 3.000 MAGLITE DE (processing aids) 0.510 STRUTKOL 40MS 3.000 N339C/B (carbon black) 90.000 BARYTES 30.000 PROPAR 100 OIL 10.000(Paraffinic/napthenic oil) STRUTKOL WB222 3.000 (blend of fatty acids)ZINC OXIDE 3.000 T.M.T.D.S. 1.000 (tetramethylthiuram disulphide)M.B.T.S. (2,2 dithiobisbenzothiazole) 2.000 TOTAL 246.510

The term parts per hundred defines the weight of the other components asa percentage of the weight of polymer. Applicant submits that thismeasure would be well known to persons skilled in the art and need notbe described in further detail.

The formulation excluding curing agents and blend of fatty acids ismixed in an internal mixer. The processing aids assist in mixing thecarbon black homogenously into the chlorobutyl polymer. The componentsare largely in the form of flowable solids except for oil which isnaturally liquid.

The rubber formulation is then dumped from the internal mixer into anopen mill mixer. The rubber which is soft and pliable/formable is thenpassed between two rollers in the open mill mixer to form sheeting whichcomprises the master batch. The mixing process is exothermic and as aresult of this process the rubber heats above 100° C.

The master batch is then allowed to cool for 24 hrs and thereafter it isreturned to the open mill mixer and this warms the mixture up. Furtherthe accelerators are added to the mixture and it is mixed thoroughly.The mix is then passed through the rolls and the final mix is sheetedoff in sheet form and permitted to cool in a tray.

Thereafter the rubber is extruded into solid cylindrical rods ofapproximately 30 mm diameter. The rubber is not yet vulcanised at thistime as the vulcanisation process proceeds slowly at the mixingtemperatures. These rods are then chopped into blanks by means oftransverse slices of the required spacing. The blanks are then placed ina mould for moulding the core of the golf ball.

The blanks are cut slightly larger than the mould so that there is somecompressive pressure when they are received in the mould. Any excessmaterial squeezes out of the mould during the moulding process. Therubber is then moulded in the mould by heating to a temperature of about160° C. in a thermosetting process for a time period of 3 to 7 minutes.During this period vulcanisation eg cross linking takes place.

The inner core can then be removed from the mould. Thereafter a SURLYNcover can be applied to the inner core to produce or yield a finishedgolf ball product with a dimpled outer surface. This is done by aninjection moulding process.

EXAMPLE 2

The formulation used in Example 2 is shown in the table below.

PHR INGREDIENT (parts per hundred of the polymer) X2 BROMOBUTYL 100.000STEARIC ACID 1.000 MICROWAX (micro-crystalline wax) 3.000 MAGLITE DE(processing aids) 0.510 STRUTKOL 40MS 3.000 N339 C/B (carbon black)90.000 KAOLIN HR1 50.000 PROPAR 100 OIL 10.000 (Paraffinic/napthenicoil) STRUTKOL WB222 3.000 (blend of fatty acids) ZINC OXIDE 3.000T.M.T.D.S. 1.000 (tetramethylthiuram disulphide) M.B.T.S. (2,2dithiobisbenzothiazole) 2.000 TOTAL 266.510

The formulation was used as with Example 1 to produce a core for a golfball. Balls produced with the formulation in Examples 1 and 2 were thentested on the applicant's indoor golf game.

Further example formulations were made with N220 carbon black and werefound to produce even better results. Some of these further examplesomitted kaolin and barytes but were otherwise of similar composition toExamples 1 and 2.

The golf ball described above with reference to the examples undergoesan appropriately high energy loss when struck against a wall andconsequently the rebound distance is diminished. This is due to thespecific halo butyl polymer/carbon black mixture which is used. Bycontrast a normal golf ball undergoes substantially less energy losswhen it rebounds off a wall.

An advantage of the ball described above is that it producesreproducible rebound characteristics off a rebound wall for varyingtemperature conditions. Further the rebound properties of the ball donot alter as the game is played such that there is no significantincrease in rebound after the game has been played for 15 or 20 minutes.

It will of course be realised that the above has been given only by wayof illustrative example of the invention and that all such modificationsand variations thereto as would be apparent to persons skilled in theart are deemed to fall within the broad scope and ambit of the inventionas is herein set forth.

What is claimed is:
 1. A golf ball comprising: a molded resilient innercore made of a rubber compound, said rubber compound comprising ahalo-butyl rubber polymer and a carbon black filler; and a polymericcover surrounding the inner core, wherein the carbon black filler ispresent in an amount of between 80% to 100% by weight of the rubbercompound.
 2. A golf ball according to claim 1, wherein the carbon blackcomprises 88% to 92% by weight of the total rubber component.
 3. A golfball according to claim 1, where the cover is dimpled.
 4. A golf ballaccording to claim 1, wherein the cover is made of an ionomeric polymercompound.
 5. A golf ball according to claim 1, wherein the halo-butylrubber polymer is either a chlorobutyl rubber polymer or bromobutylrubber polymer.
 6. A golf ball according to claim 1, wherein the carbonblack comprises 85% to 95% by weight of the total rubber component.
 7. Agolf ball according to claim 1, wherein the rubber compound has beenvulcanized by a sulphur compound.
 8. A golf ball according to claim 7,wherein the sulphur compound is a disulphide compound.
 9. A golf ballaccording to claim 8, wherein the disulphide compound is selected fromthe group consisting of tetramethylthiuramdisulphide,2-dithiobisbenzothiazole, and mixtures thereof.
 10. A golf ballaccording to claim 1, wherein the rubber compound has been vulcanised byzinc oxide and at least one disulphide compound.
 11. A golf ballaccording to claim 10, wherein the at least one disulphide compound isselected from the group consisting of tetramethylthiuramdisulphide,2-dithiobisbenzothiazole, and mixtures thereof.
 12. A golf ballaccording to claim 1, wherein the rubber compound has been vulcanized bya vulcanizing agent selected from the group consisting of zinc oxide,disulphide compound, and mixtures thereof.
 13. A golf ball according toclaim 1, wherein the rubber compound further comprising a blend of fattyacids.
 14. A golf ball according to claim 13, wherein the blend of fattyacids comprises at least stearic acid.
 15. A golf ball according toclaim 1, wherein the rubber compound further comprising paraffinic oiland/or naphthenic oil.
 16. A golf ball according to claim 1, wherein therubber compound further comprises micro-crystalline wax.
 17. A golf ballaccording to claim 1, wherein the rubber compound further comprisesbarytes and/or kaolin.
 18. A golf ball according to claim 1, wherein therubber compound further comprises one or more components selected fromthe group consisting of a blend of fatty acids, stearic acid, paraffinicoil, naphthenic oil, micro-crystalline wax, barytes and kaolin.
 19. Agolf ball according to claim 5, wherein the rubber compound furthercomprises one or more components selected from the group consisting of ablend of fatty acids, stearic acid, paraffinic oil, naphthenic oil,micro-crystalline wax, barytes and kaolin.
 20. A golf ball according toclaim 12, wherein the rubber compound further comprises one or morecomponents selected from the group consisting of a blend of fatty acids,stearic acid, paraffinic oil naphthenic oil, micro-crystalline wax,barytes and kaolin.
 21. A golf ball comprising: a moulded resilientinner core made of a rubber compound, said rubber compound comprising ahalo-butyl rubber polymer and a carbon black filler; and a polymericcover surrounding the inner core, wherein the rubber compound has beenvulcanized by a sulphur compound.